Metal stress memorization technology

ABSTRACT

A semiconductor device and method for manufacturing a tensile strained NMOS and a compressive strained PMOS transistor pair, wherein a stressor material is sacrificial is disclosed. The method provides for a substrate, which includes a source/drain for an NMOS transistor, and a PMOS transistor. A first barrier layer is formed on the substrate and a first stressor material is formed on the first barrier layer. The first barrier layer is selectively removed from the PMOS transistor. The substrate is flash annealed and the remaining first stressor material and barrier layer is removed from the substrate.

TECHNICAL FIELD

The present invention relates generally to semiconductor devices, andmore particularly to a structure and a method for manufacturing atensile strained NMOS and a compressive strained PMOS transistor pair.

BACKGROUND

Classical semiconductor scaling, typically known as a device shrink, iscurrently supplemented by effective scaling, using techniques such asstress memorization. With circuits becoming smaller and faster,improvement in device drive current (I_(on)) is becoming more important.Drive current is closely related to gate length, gate capacitance, andcarrier mobility. Stress memorization techniques are being used to speedcarrier mobility in transistor channels, enabling higher drive currents.

Stress or strain in a device may have components in three directions,parallel to the metal-oxide-semiconductor (MOS) device channel length,parallel to the device channel width, and perpendicular to the channelplane. The strains parallel to the device channel length and width arecalled in-plane strains. Research has revealed that a bi-axial, in-planetensile strain field can improve NMOS (n-channel MOS transistor)performance, and compressive strain parallel to channel length directioncan improve PMOS (p-channel MOS transistor) device performance.

One way to develop strain is by using a graded SiGe epitaxy layer as asubstrate on which a layer of relaxed SiGe is formed. A layer of siliconis formed on the relaxed SiGe layer. MOS devices are then formed on thesilicon layer, which has inherent strain. Since the lattice constant ofSiGe is larger than that of Si, the Si film is under biaxial tension andthus the carriers exhibit strain-enhanced mobility. The lattice spacingmismatch between the SiGe layer causes the underlying layer to developan in-plane stress to match the lattice spacing. This additionalprocessing may add cost to the semiconductor device manufacturingprocess.

Strain can also be applied by forming a strained capping layer, such asa barrier layer, on a MOS device. However, the barrier layer may notproduce sufficient stress to produce the desired results. Theconventional method of forming strained capping layers, suffersdrawbacks, and the effect is limited by the properties of the cappinglayer. For example, the thickness of the strained capping layer islimited due to the subsequent gap filling difficulty caused by the thickcapping layer. Therefore, the strain applied by the capping layer islimited. In addition, forming a strained capping layer that hascustomized strains for different devices, such as PMOS and NMOS devices,is particularly complex and costly.

SUMMARY OF THE INVENTION

These and other problems are generally solved or circumvented, andtechnical advantages are generally achieved, by illustrative embodimentsin which stress memorization layers within semiconductor devices andmethods of manufacturing stress memorization layers within semiconductordevices are presented.

Semiconductor devices are manufactured by forming active regions in asemiconductor substrate, depositing various insulating, conductive, andsemiconductive layers over the substrate, and patterning them insequential steps. In accordance with an illustrative embodiment, asubstrate is provided, which includes a source/drain for an NMOStransistor, and a PMOS transistor. A first barrier layer is formed onthe substrate and a first stressor-material is formed on the firstbarrier layer. The first stressor-material and the first barrier layeris selectively removed from the PMOS transistor. The substrate may beflash annealed and the remaining first stressor-material and firstbarrier layer is removed from the substrate.

Another illustrative embodiment provides a substrate, wherein thesubstrate includes a source/drain for a NMOS transistor and a PMOStransistor, and wherein the substrate further includes a metal silicidelayer. A second barrier layer is formed on the metal silicide layer. Asecond stressor-material is deposited on the second barrier layer. Asecond flash anneal is implemented and the stressor-material is removedfrom the substrate.

In accordance with yet another illustrative embodiment, a semiconductordevice with enhanced carrier mobility comprises an NMOS device with afirst stress value and a PMOS device with a second stress value, whereina stressor layer is sacrificial.

An advantage of the illustrative embodiments of the present invention isenhanced carrier mobility and increased transistor drive current. Afurther advantage of the illustrative embodiments of the presentinvention is a low cost implementation of a stress configuration, whichmay be optimized for increased transistor drive current.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter, which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiments disclosed may be readily utilized as a basisfor modifying or designing other structures or processes for carryingout the same purposes of the present invention. It should also berealized by those skilled in the art that such equivalent constructionsdo not depart from the spirit and scope of the invention as set forth inthe appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram of preferred NMOS and PMOS stress configurations;

FIG. 2 is a process flow illustrating an embodiment of athermal/mechanical stress memorization method during dopant activationanneal;

FIG. 3 shows cross-sectional views of a substrate undergoing anembodiment of a thermal/mechanical stress memorization method duringdopant activation anneal;

FIG. 4 is a process flow illustrating another embodiment of athermal/mechanical stress memorization method during second silicideanneal;

FIG. 5 shows cross-sectional views of a substrate undergoing anotherembodiment of a thermal/mechanical stress memorization method duringsecond silicide anneal; and

FIG. 6 is a process flow illustrating yet another embodiment of athermal/mechanical stress memorization method during dopant activationanneal and second silicide anneal.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the preferredembodiments and are not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently preferred embodiments arediscussed in detail below. It should be appreciated, however, that thepresent invention provides many applicable inventive concepts that canbe embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention.

The present invention will be described with respect to illustrativeembodiments in a specific context, namely a CMOS configuration. Theinvention may also be applied, however, to bipolar and bi-CMOSstructures.

An illustrative embodiment shows a stress memorization technique thatmay stress the film, then activate the dopants causing an impurityrearrangement; stress the film and control poly grain growth; and/orstress the film and form silicide. Another illustrative embodiment maythermally stress the film during dopant activation, poly grain growth,and silicidation.

The stress in the film due to differences in thermal expansioncoefficients isσ_(f)=((α_(s)−α_(f))ΔT(Y _(f)/1−ν_(f)))where σ_(f) is thermal stress, Y_(f) is Young's modulus, ν_(f) isPoisson's ratio, α_(s) is the substrate coefficient of thermal expansionand α_(f) is the film coefficient of thermal expansion. The illustrativeembodiments present a method of using the differences in thermalexpansion between materials to stress semiconductor active regionsduring substrate processing.

With reference now to FIG. 1, there is shown a diagram of illustrativeNMOS and PMOS stress configurations. The substrate 100 may comprisesilicon or other semiconductor material covered by an insulating layer,for example. The substrate 100 may also include other active componentsor circuits formed in the front end of line (FEOL), not shown. Thesubstrate 100 may comprise silicon oxide over single-crystal silicon,for example. The substrate 100 may include other conductive layers orother semiconductor elements, e.g. transistors, diodes, etc. Compoundsemiconductors, GaAs, InP, Si/Ge, or SiC, as examples, may be used inplace of silicon.

NMOS transistor 102 has an N-channel region 104 and source drain regions106 and 108, respectively. NMOS transistor 102 displays increasedelectron mobility if the N-channel region 104 of the transistor is undertensile strain, as indicated by arrows 109. Moving the silicon atomsfarther apart reduces the atomic forces that interfere with the movementof electrons through the transistors, subsequently resulting in bettersemiconductor device performance and lower energy consumption.

PMOS transistor 110 has a P-channel region 112 and source drain regions114 and 116 respectively. The PMOS transistor displays increased holemobility, if the p-channel region is under compressive stress, indicatedby arrows 117.

To create the regions with sufficient stress in the NMOS and PMOSchannel regions, a combination of stress techniques may be used with abetter effect than a single technique. The mechanical stress of astressor layer on the active channel plus the thermal stress ofprocessing may be applied at more than one step in the semiconductormanufacturing process. The stress produced by multiple techniques isadditive. Therefore, the device characteristics produced by additivetechniques may show an enhanced improvement.

FIG. 2 is a process flow illustrating an embodiment of athermal/mechanical stress memorization method. A semiconductor substrateis provided, such as substrate 100 in FIG. 1, which includes active andinactive regions. Within the active regions, the NMOS and PMOS devicesare defined. The process begins following the spacer formation andimplantations of the source drain areas of the NMOS and PMOS structures.An optional pre-amorphization implant (PAI) utilizing a neutral ion,such as silicon (Si), germanium (Ge), and/or xenon (Xe) may beperformed. As an example, Ge ions are accelerated to an energyappropriate to form amorphous regions in targeted areas. Ionimplantation devices, such as, devices manufactured by Varian Company,Palo Alto, Calif., Genius Company, and Applied Materials, Inc. can beused to provide the amorphization implant as well as the dopantimplants. The PAI process may be selectively performed on NMOStransistor structures.

Following the processes above, a barrier layer is formed (step 202). Thebarrier layer may be formed of SiO₂. In another embodiment, the barrierlayer may be comprised of, for an example, a layer of low-temperatureand high tensile nitride (Si₃N₄) film. The stress level of a nitridefilm may be adjusted by the type of starting material used to make thenitride film and the type of nitrogen-containing gas treating thestarting material. The set of chemical vapor deposition (CVD) conditionsunder which the film is grown and/or a thickness to which the film isgrown also determines the stress level of the nitride film. Anammonia-treated BTBAS film may provide a high-stress property, and maymaintain the stress property during anneal. Relying on the stress levelof a nitride film alone, however, may not be sufficient to produce thedesired stress levels in the silicon device. Therefore, astressor-material may be formed on the barrier layer to provideadditional stress.

A stressor-layer formation (step 204) follows the barrier layerformation. The stressor-material layer may be a metal or metalcombination such as, for example, TiN, Co, Ni, W, Ti, Ta, Mo, and thelike. The thermal expansion coefficient of the stressor-material layermay be greater than the thermal expansion coefficient of Silicon by 20%.See the table of thermal expansion coefficients listed below:

Thermal expansion Material coefficient - α (10⁻⁶ K⁻¹) TiSi2 12.5 CoSi210.4 NiSi 16.0 Si 2.3 SiO2 0.5 TiN 9.3 Si₃N₄ A FUNCTION OF FORMATION ANDTHICKNESS TYPICALLY < 4.0

The stressor-material layer and the barrier layer may then beselectively removed from the PMOS region (step 206). Optionally thebarrier layer may stay in place over the PMOS region.

The substrate is annealed at a temperature preferably greater than 400C. (step 208). The anneal may be a spike, flash, or laser anneal. Thedifferences between spike, flash and laser anneal processes are known inthe art and may be seen in temperature versus time graphs.

Following anneal, the residual barrier layer and stressor-material layermay be removed (step 210). Thereinafter, the substrate may continueconventional processing.

FIGS. 3 a-3 c are cross-sectional views of an illustrative embodiment ofthe process steps presented in FIG. 2. FIG. 3 a illustrates across-sectional view of substrate 300 following a stressor-materiallayer formation, such as step 204 in FIG. 2.

Substrate 300 is a semiconductor device substrate such as substrate 100in FIG. 1. NMOS transistor 302 has an N-channel region 304, gate stack305, spacers 307, and source drain regions 306 and 308, respectively.PMOS transistor 310 has a P-channel region 312, gate stack 313, spacers315, and source drain regions 314 and 316 respectively. A barrier layer320 is deposited on the NMOS transistor region 302 and the PMOStransistor region 310. Layered over the barrier layer 320, astressor-material layer 322 is disposed.

FIG. 3 b shows a cross-sectional view of the NMOS and PMOS transistorregions following a selective removal step such as selective removalstep 206 of FIG. 2. The cross-sectional view shows the PMOS region 310with barrier layer 320 and the stressor-material layer 322 selectivelyremoved. The selective removal of barrier layer 320 andstressor-material layer 322 on PMOS 310 may be performed to alleviatestress-induced device degradation. The barrier layer 320 and thestressor-material layer 322 remain on the NMOS substrate area. Thethermal anneal, such as step 208 of FIG. 2, may be accomplished with thebarrier layer 320 and the stressor-material layer 322 configured asshown in FIG. 3 b.

FIG. 3 c illustrates substrate 300 following the removal of the residualstressormaterial layer 322 and barrier layer 320. It should be notedthat the stressor-material layer and barrier layer may be sacrificiallayers in this embodiment.

FIG. 4 is a process flow illustrating another embodiment of athermal/mechanical stress memorization method. The process begins with asilicide metal deposition (step 402). Titanium silicide (TiSi₂) is acommon silicide and is an example of a silicide that may be used. Othersilicides that may be used include CoSi₂, TaSi₂, MoSi₂, Ni_(x)Si_(y),and PtSi. Silicides may be used in CMOS technology to reduce sheetresistance of polysilicon lines and n+ regions. The formation ofsilicides can be done in two general ways: by direct deposition of thesilicide or by deposition of the metal on top of Si followed by thereaction between the metal and Si to form the silicide. The directdeposition method can be accomplished, as an example, by sputtering froma composite target, co-sputtering from two targets of the metal and Si,co-evaporation of the metal and Si, and CVD. These methods are withinthe scope of the illustrative embodiments.

However, the reaction method is implemented in this embodiment. Themetal, Ti for example, may be deposited by sputtering on the exposedgate and/or source drain regions, all of which are silicon. Theunreacted metal is then selectively etched away. This method producesself-aligned silicide structures on the gate and/or source drains.

The substrate undergoes a first silicide anneal (step 404), and thesilicide forming reaction occurs wherever the silicon and metal are incontact, that is in this example, on the gate and source/drain regions.Separate silicidation steps, such as silicidation of the source/drainregions separately from the gate stack regions are known within the artand are within the scope of these embodiments. The first silicide annealis followed by a barrier layer formation (step 406). The barrier layermay be comprised of a SiO₂ or a Si₃N₄. A stressor-material layer is thendisposed (step 408). The stressor-material layer may be a metal or metalcombination such as, for example, TiN, Co, Ni, W, Ti, Ta, Mo, and thelike. The stressor material may have a thermal expansion coefficientgreater by 20% than the thermal expansion coefficient of silicon. Thestressor-material may have a thermal expansion coefficient greater thanthe silicide layer.

The stressor-material layer is selectively removed from the PMOS (step410). The substrate undergoes a second silicide anneal (step 412). Thesecond silicide anneal step may be implemented in a spike, flash, orlaser anneal. The second silicide anneal is preferably implemented at atemperature greater than 350 C. and greater than the first silicideanneal. Thereinafter the substrate may continue conventional processing.

FIGS. 5 a-5 c show cross-sectional views of a substrate undergoinganother embodiment of a thermal/mechanical stress memorization method.Turning to FIG. 5 a, substrate 500 is a semiconductor device substratesuch as substrate 100 in FIG. 1. NMOS transistor 502 has an N-channelregion 504, gate stack 505, spacers 507, and source drain regions 506and 508, respectively. Gate stack 505 and source drain regions 506 and508 show silicided regions 509. PMOS transistor 510 has a P-channelregion 512, gate stack 513, spacers 515, and source drain regions 514and 516 respectively. Gate stack 513 and source drain regions 514 and516 show silicided regions 509. A barrier layer 520 is deposited on theNMOS transistor region 502 and the PMOS transistor region 510, as instep 406 of FIG. 4. Layered over the barrier layer 520, astressor-material layer 522 is disposed, as in step 408 of FIG. 4.

FIG. 5 b shows a cross-sectional view of the NMOS and PMOS transistorregions following a selective removal step such as selective removalstep 410 of FIG. 4. The cross-sectional view shows the PMOS region 510with barrier layer 520 and the stressor-material layer 522 selectivelyremoved. The selective removal of barrier layer 520 andstressor-material layer 522 on PMOS 510 may be performed to alleviatestress-induced device degradation in the PMOS transistor. The barrierlayer 520 and the stressor-material layer 522 remain on the NMOSsubstrate area. The second silicide anneal, such as step 412 of FIG. 4,may be accomplished with the barrier layer 520 and the stressor-materiallayer 522 configured as shown in FIG. 5 b.

FIG. 5 c illustrates substrate 500 following the removal of the residualstressor-material layer 522. It should be noted that thestressor-material layer may be a sacrificial layer in this embodiment.However, the barrier layer 520 remains in place.

FIG. 6 is a process flow illustrating yet another embodiment of athermal mechanical stress memorization method. This embodiment adds thestress memorized from a first embodiment discussed above to the stresscreated by a second embodiment discussed above. The stress effect isadditive. The process-induced stress significantly influences thetransistor device performance.

The process begins following spacer formation and source drain implants.A pre-amorphous implant (PAI) may optionally be included in the process.A first barrier layer is formed (602). The first barrier layer may be aSiO₂ layer or a Si₃N₄ layer such as layer 320 in FIG. 3. Next, astressor-material-1 layer is formed on the first barrier layer (step604). The stressor-material-1 may be Co, Ni, W, Ti, Ta, Mo, or the like.The selective removal of the stressor-material-1 and barrier layer onPMOS structure follows (step 606). The polysilicon is annealed andsource/drain regions are activated in dopant activation anneal (step608). The residual stressor-material-1 layer and first barrier layer isthen removed (step 610). A metal deposited for silicide formation (612)follows, such as the metal deposited in step 402 in FIG. 4. The firstsilicide anneal is implemented (step 614), such as the first silicideanneal in step 404 of FIG. 4. On top of the silicide layer, a secondbarrier layer is formed (step 616). A stressor-material is thendeposited (step 618). The stressor-material layer is then selectivelyremoved (step 620) from the PMOS transistor region. The second silicideanneal is implemented (step 622), such as step 412 in FIG. 4. Theresidual stressor-material-2 layer is then removed (step 624), thusending the process.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions, andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims. For example,many of the features and functions discussed above can be implemented insoftware, hardware, or firmware, or a combination thereof. As anotherexample, it will be readily understood by those skilled in the art thatfilm thicknesses may be varied while remaining within the scope of thepresent invention.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present invention, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present invention. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

1. A method of manufacturing a semiconductor device comprising:providing a substrate, wherein the substrate includes a source/drain foran NMOS transistor and a source/drain for a PMOS transistor; forming afirst barrier layer on the substrate; forming a first stressor-materialon the first barrier layer; selectively removing the firststressor-material from the PMOS transistor; selectively removing thefirst barrier layer from the PMOS transistor; annealing the substrate ina dopant activation anneal; removing the remaining firststressor-material; removing the remaining first barrier layer, therebyimplementing a first stress process; following the first stress process,forming a second barrier layer on a metal silicide layer formed on thesubstrate; depositing a second stressor-material on the second barrierlayer; performing a second silicide anneal on the substrate; andselectively removing the second stressor-material.
 2. The method ofclaim 1, wherein the dopant activation anneal is implemented at atemperature higher than 400° C.
 3. The method of claim 2, wherein thedopant activation anneal is selected from a group consisting of a spikeanneal, a flash anneal, and a laser anneal.
 4. The method of claim 1,wherein the first stressor-material has a thermal expansion coefficient(α) greater than a thermal expansion coefficient of silicon (α_(si)) byat least 20%.
 5. The method of claim 1, wherein the first barrier layeris selected from a group consisting of oxide, nitride, oxynitride, andcombinations thereof.
 6. The method of claim 1, further comprising:implanting a pre amorphizing implantation into the NMOS transistorbefore forming the first barrier layer.
 7. The method of claim 6,wherein the pre amorphizing implantation is implemented with a speciesselected from a group consisting of Si, Ge, and Xe ions.
 8. The methodof claim 1, wherein the second stressor-material is selected from agroup consisting of Co, Ni, W, Ti, Ta, and Mo.
 9. The method of claim 1,wherein the metal silicide, layer is chosen from a group consisting ofnickel silicide, cobalt silicide, and titanium silicide.
 10. The methodof claim 1, wherein the second silicide anneal is implemented at atemperature higher than 350° C.
 11. The method of claim 1, wherein thesecond silicide anneal is implemented at a temperature higher than animplemented first silicide anneal.
 12. The method of claim 1, whereinthe second silicide anneal is selected from a group consisting of aspike anneal, a flash anneal, and a laser anneal.
 13. A method ofmanufacturing a semiconductor device comprising: providing a substrate;forming a barrier layer on the substrate; disposing a stressor-materialon the barrier layer, wherein the stressor-material has a metal materialwith a thermal expansion coefficient (α) greater than a thermalexpansion coefficient of silicon (α_(si)) by at least 20%; selectivelyremoving the stressor-material; performing an anneal on the substrate;removing the residual stressor-material; removing the barrier layer tocomplete a first stress process; following the first stress process,forming a second barrier layer on a metal silicide layer formed on thesubstrate; depositing a second stressor-material on the second barrierlayer; performing a second silicide anneal on the substrate; andselectively removing the second stressor-material.
 14. The method ofclaim 13, further comprising: implanting a pre amorphizing implantationinto the semiconductor device before forming the barrier layer.